Three-dimensional modeling of structures by a computer can be useful for a wide range of applications. Common applications relate to the generation of virtual structures to produce a visual display that depicts the structure. For example, video games often generate in-game characters using virtual models that recreate the motions of real-world actors, athletes, animals or other structures. Similar efforts are often undertaken for computer-generated characters in movies, television shows and other visual displays. The useful applications span areas as diverse as medicine, activity recognition, and entertainment. As robots become more commonplace in settings that include humans, they will need the ability to recognize human physical action.
Increasingly, virtual modeling is moving away from the creation of a cartoon style appearance to more of a photo-realistic display of the virtual sets and actors. It can still take a tremendous effort to create authentic virtual doubles of real-world actors. Creation of a model that captures the muscle, joint, neurological and other intricacies of the human body is a prohibitively difficult proposition due to the sheer number of factors involved. Thus, modeling of a person is often implemented using motion capture of a real-world person. While in recent years, algorithms have been proposed that capture full skeletal motion at near real-time frame rates, they mostly rely on multi-view camera systems and specially controlled recording conditions which limit their applicability. It remains one of the biggest challenges to capture human performances, i.e., motion and possibly dynamic geometry of actors in the real world in order to map them onto virtual doubles.